Tire Size Calculator interactive tool
1Current / Factory Tire
2New / Target Tire
Speedometer Impact
With Tire 2, when your speedometer reads 60 mph, your actual speed will be 62.2 mph.
Diameter variance: +3.7%. (Variances greater than 3% are generally not recommended as they can affect ABS and brake systems).
What Is Tire Size?
A tire size calculator helps automotive enthusiasts, mechanics, and everyday drivers decode complex metric tire designations. This wheel size calculator is primarily used when someone wants to change the size of their wheels or tires without negatively impacting their vehicle's performance or safety.
How to Read a Metric Tire Size
Look at the sidewall of your tire. You will see a sequence similar to 225/65R17.
- 225 (Section Width): The width of the tire from sidewall to sidewall, measured in millimeters.
- 65 (Aspect Ratio): The height of the tire's sidewall, expressed as a percentage of the width. In this case, the sidewall height is 65% of 225mm.
- R (Construction): Stands for Radial construction (the industry standard).
- 17 (Wheel Diameter): The size of the wheel (rim) the tire is designed to fit, measured in inches.
The Danger of Changing Tire Sizes: Will These Tires Fit My Car?
Your vehicle's computer systems—including the speedometer, odometer, anti-lock brakes (ABS), and traction control—are all calibrated to the factory tire's overall circumference.
If you install larger tires, your vehicle will travel farther with every revolution of the wheel, which can change speedometer readings. This tire comparison calculator shows the dimensional difference between two sizes. A small percentage difference does not by itself confirm safe fitment, so check clearance, load rating, speed rating, and the vehicle manufacturer's specifications before changing sizes.
How To Use the Tire Size Calculator
- Enter the current tire width (e.g., 225), aspect ratio (e.g., 65), and wheel diameter (e.g., 17) in the 'Current Tire' section.
- Review the calculated tire dimensions in inches, including overall diameter, section width, and circumference.
- If comparing two tires, enter the second size in the 'New Tire' section to see the difference in speedometer readings and clearance.
- Use the comparison as a dimensional reference, then confirm clearance, load rating, and fitment with the vehicle manufacturer or a tire professional.
Compare tire sizes and speedometer difference
This tire size calculator compares width, sidewall, overall diameter, circumference, and the modeled speedometer difference between two tire codes. Dimensional comparison does not confirm vehicle clearance, load rating, or fitment.
Need the formula or convention behind this result? Read the calculator methods and assumptions.